The Korean Longitudinal Study of Aging (KLoSA) is a nationally representative survey of older persons in the Republic of Korea, with an emphasis on work, health, cognition, family, and socioeconomic circumstances. It is the country's only multidisciplinary panel study, interviewing more than 10,000 respondents at least 45 years of age biennially since 2006. It was purposefully designed with the Health and Retirement Study (HRS) as a model to enable cross-country analyses. We have successfully completed six waves of longitudinal, face- to-face interviews and have released anonymized data to the wider research community together with a user- friendly harmonized data file for cross-country analysis. From its inception, cognition has been an important component of the core survey, including both the Mini Mental State Exam and informant interviews with close relatives of those not able to complete cognitive tests. Building on this strong foundation, we now aim to assess dementia and cognitive impairment without dementia (CIND) of Korean older adults, using the HRS Harmonized Cognitive Assessment Protocol (HCAP). Specifically, we aim to administer the full HCAP protocol to a random half of KLoSA respondents aged 65 and older (about 2,000 respondents) by sending well-trained interviewers to their homes. HCAP consists of in-depth cognitive tests, assessment of functional and mental health conditions, and informant reports. As the HCAP algorithm for dementia and CIND classification is developed within the U.S. context, we aim to validate the HCAP algorithmic diagnosis with clinical assessment. For a subsample (about 300 respondents), we aim to collect neuroimaging data, following the Alzheimer's Disease Neuroimaging Initiative (ADNI) 3 protocol. We will identify brain structures and functions that characterize cognitive reserve and make cognitive and neuroimaging data widely available through the Global Alzheimer's Association Interactive Network (GAAIN) to contribute to the advancement of the neuroscience of Alzheimer's disease. We will link all newly collected data to the on-going KLoSA main survey and make these enriched data available to the wider research community. Our harmonized protocol for assessment of dementia and late-life cognition will enable researchers to compare results in Korea with those in the United States, England, Mexico, China, India, and other countries that implement the HRS HCAP protocol.